This invention relates generally to nuclear reactors and more particularly to a poison and dilution system for preventing supercriticality in nuclear power plants in the event of core disruptive accidents which result in core meltdown, and which is operational independently of the final reactor orientation.
Since the inception of the commercial nuclear power industry, prime concern of all parties involved has been safety. Regulatory bodies, commercial manufacturers, and others have spent vast sums of money in research, design, and development of redundant systems of assuring the safety of the public.
Regulatory bodies define the design requirement of at least a large portion of nuclear reactor plants in terms of accidents which have been experienced in the field and also in terms of hypothetical accidents which may be experienced in the nuclear industry. One such hypothetical accident is based on assumptions resulting in the melting of a portion of the reactor core and its related components into a flowing configuration. Under such hypothetical conditions, apparatus must be provided to prevent any combination of molten fuel into a large, supercritical assembly.
Prior art has generally prevented this combination into a supercritical assembly by containing the molten fuel in separate areas. These apparatus are generally located at the bottom of the reactor pressure vessel, and because of their structure and function, are commonly called core-catchers.
With the advent of the energy crisis, the use of nuclear energy to replace fossil fuels is being widely investigated. Among the various fields being investigated for possible conversion to nuclear energy is the transportation field. Prime contenders for conversion in this field include ships, airplanes and railroad trains.
As with conventional nuclear power plants, the design of these mobile power plants must take into account hypothetical accidents. Included within these postulated accidents is the possibility of a nuclear core meltdown. In addition to accidents occurring during normal full power operation, such as with the loss of reactor coolant, reactor core meltdown can also occur due to the decay heat of the fission products after reactor shutdown. Designing the power plant against accidents which leaves the core intact, therefore, is not sufficient. The possible recombination of molten fuel must also be prevented.
In addition to normal accidents arising during nuclear operation, mobile nuclear power plants must also be designed to guard against accidents which may occur because of the mobile nature of the power plants. One such type of accident, which is not a concern in the design of conventional nuclear power plants, is an impact accident; for example, the crash of an airborne nuclear power plant into the earth. A major problem with this type of accident is that the orientation of the nuclear power plant after the accident is unknown. Except in the event of violent seismic incidents, conventional nuclear power plants can utilize core catchers placed at the bottom of the reactor vessels because it is known in which direction the molten fuel will flow. This type of apparatus is not possible for mobile power plants, because until the actual accident occurs, it is not possible to determine which section of the power plant will be "down".
Another problem associated with preventing the supercriticality of the fuel in the event of a core meltdown in mobile power plants is weight. Because of their mobile nature, one of the most important design considerations is weight. Any system designed to prevent supercriticality of the molten fuel must not add so much weight that, taken in conjunction with the rest of the power plant, the power plant weighs too muct to be mobile.